Wood pallets are typically constituted by a loading deck, which comprises one or two layers of strips arranged side by side and superimposed so that the strips of one layer are parallel to each other and are optionally perpendicular to the strips of the other layer, and by feet or blocks or lower blocking elements designed to keep the loading deck raised with respect to the resting surface.
In many cases there are three rows of blocks and each row is composed of three blocks which are mutually spaced so as to allow the pallet to be moved by virtue of lifting means on any of its four sides.
Generally, the pallet has a rectangular plan shape and the blocks are mutually connected not only by the resting surface but also by bottom strips.
Pallet assembly operations are normally performed by using nailing machines.
One known solution provides for the use of nailing apparatuses, of an exclusively mechanical type, which are constituted by stems which can be moved along a movement direction which is vertical and perpendicular to the plane of arrangement of the lumber to be assembled, and are adapted to drive the nails into the wood bodies.
Since very often the wood pieces to be assembled have even significantly different height dimensions, if a purely mechanical nailing head is used, incorrect insertion of the nails in the lumber can occur, because the nail might either penetrate excessively into the wood or the head of the nail might remain protruding from the flat surface of the lumber.
In order to try to solve this drawback, nailing machines have been proposed which are provided with hydraulically actuated nailing heads.
Another known solution, disclosed and claimed in IT 1392697 in the name of this same Applicant, provides for the use of nailing heads for the assembly of wood pieces which have a slider for the actuation of nailing stems which can move, along a substantially vertical movement direction, by means of a linkage-crank assembly actuated by a motor.
In particular, the linkage is composed of a rod which is functionally connected to the upper rotation pivot and is provided, at its free end, with a piston body which can translate within a cylinder provided with a chamber that accommodates an elastically deformable product such as a spring or a gas.
In turn, the cylinder is connected to the lower rotation pivot of the slider.
By virtue of the presence of the elastic product inside the cylinder, the penetration of the nails does not depend only on the position of the crank as in purely mechanical classic nailing heads. In fact, by virtue of the deformable elastic product, the descending motion of the rod is limited by the thickness of the wood.
Although this constructive solution is particularly advantageous from the theoretical standpoint, it has some drawbacks, especially in terms of costs and constructive complexity.
It is in fact evident that it is necessary to act constructively on each nailing head by associating a cylinder with each linkage.